In kilns of the type contemplated by the present invention each kiln outlet has a tubular support to which the inlet end of the associated cooler tube is attached and a steel reinforcing ring within the support. Insulation is provided between the ring and the support and the ring is lined internally with a wear-resisting ceramic material.
In a typical rotary kiln having a plurality of such outlets, it is well known to reinforce the outlets with a reinforcing frame in the form of a ring or a bush of special steel, in such a way that its axially inner end relative to the kiln is substantially flush with the kiln lining. Since the action of the hot clinker within the kiln when in use is detrimental to the ring, it is normally lined internally with a heat-resistant, wear-resistant material which is cast on the inside of the ring and secured to the ring by suitable bracing elements. The axially inner edge of the ring can also be recessed relative to the kiln lining and coated with a ceramic material flush with the kiln lining.
Inasmuch as the steel ring and the kiln lining material expand at different rates as a result of the inevitable heat stresses, cracks can form between the ring and kiln lining. These cracks may expose the support to detrimental heat stresses from the hot clinker material. In an attempt to avoid such crack formations, according to German published application No. DTOS No. 27 02 876, the steel ring is provided with a braced, cast-on coat or collar of ceramic material. However, the steel ring is secured in place at its end within the support and thus longitudinal expansion of the ring caused by heating will cause the cast-on collar to be raised from its position of abutment against the kiln shell so that it can be easily knocked loose when it is hit by discharged clinker. Furthermore, hot clinker dust may also penetrate under the collar which therefore fails to fulfill its protecting effect at the critical joint between the kiln shell and the support.